Electric machines, especially A.C. or D.C. generators for motor vehicles usually are equipped with ventilating fan wheels. The fan blades are located on an outer blade circle which is held in position by a disc-like central portion having a suitable bore for receiving the shaft of the machine. The fan wheel may be mounted within or externally of the housing of the machine and is rotated by the shaft of the electric machine. The fan wheel supplies a substantially axial air stream to cool the electric generator or motor. Normally, the fan wheel has an outer blade circle with fan blades that extend in the axial direction and which are so disposed as to cause an axial air flow. The fan blades are often of one piece with a holding device which is mounted on the shaft of the machine. These fan wheels may be of plastic with metal inserts to increase the rigidity. Also known are fan wheels made entirely of aluminum, for example pressure castings, or simple metal foil fan wheels which are stamped out in one piece. It is a disadvantage of the known fan wheels that substantial vibration and noise generation may occur which is not caused by the air flow alone. In rotating electrical machines, electromagnetic and/or mechanical impulses may cause oscillations of the rotating members in directions parallel to the axis of rotation and these oscillations are radiated by the disc-shaped fan wheels as disturbing noises. The type of noise generation depends on the shape, the mass and the elastic properties as well as the interior damping of the fan wheel and is usually based on resonance phenomena. In order to counteract the noise generation, it is known to damp the simple metal foil fan wheels by placing on their disc-like surface damping masses. However, this step generally only shifts the generation of noise and vibration into other rpm domains.